One conventional image reading apparatus is disclosed in Japanese Patent Laid-Open No. 11-275371, but this apparatus has the following problems.
First, the apparatus has only three image sensors for R, G, and B and does not include any image sensor dedicated to monochromatic images. To process monochromatic images, therefore, a monochromatic luminance signal (Y) is generated by using the image sensors for R, G, and B. Hence, the image quality lowers owing to, e.g., positional differences between the three image sensors and differences between their spectral sensitivity characteristics.
Second, when this monochromatic luminance signal (Y) is generated directly from the outputs of the image sensors for R, G, and B, the image quality lowers owing to differences between the original reading positions of these image sensors with respect to a pixel from which a Y image is to be generated. Also, when a CCD line sensor which is generally extensively used is used as a color CCD sensor, the R, G, and B sensors are arranged in lines with certain finite intervals between them. Therefore, the image quality significantly lowers if the monochromatic luminance signal (Y) is generated directly from the outputs of these color sensors without correcting the reading position differences between the lines. Accordingly, CCD line sensors that are commonly widely used cannot be used in practice in a system which generates the monochromatic luminance signal (Y) directly from the outputs of the R, G, and B image sensors.
Third, a filter is attached to each of the R, G, and B image sensors so that each image sensor has high sensitivity to a specific wavelength when the monochromatic luminance signal (Y) is generated from these sensors. This filter reduces the quantity of light supplied to the image sensor. When the reading rate is raised, therefore, the quantity of light supplied to each image sensor further reduces, leading to a lowering of the reading accuracy.
It is an object of the present invention to provide an image reading method and apparatus capable of rapidly reading monochromatic images, realizing image quality on a desired level, and obtaining high-quality color images.
An image reading apparatus of the present invention comprises a line sensor unit including a monochromatic sensor for outputting a one-line signal by dividing the signal into a plurality of signals, and a plurality of color sensors, a mode setting circuit for setting one of a monochromatic mode and a color mode, a monochromatic analog-to-digital converter which corresponds to the monochromatic sensor and receives signals and performs analog-to-digital conversion for the received signals, a plurality of color analog-to-digital converters which correspond to the plurality of color sensors and receive signals and perform analog-to-digital conversion for the received signals, and a selector for distributing, when the monochromatic mode is set in the mode setting circuit, the plurality of output signals from the monochromatic sensor to the monochromatic analog-to-digital converter and the color analog-to-digital converters to cause the monochromatic and color analog-to-digital converters to perform analog-to-digital conversion for the signals.
When the color mode is set in the mode setting circuit, the selector can supply output signals from the color sensors to corresponding ones of the color analog-to-digital converters to cause the color analog-to-digital converters to perform analog-to-digital conversion for the signals.
The apparatus can further comprise line delaying/rearranging units which correspond to the monochromatic analog-to-digital converter and the color analog-to-digital converters, and receive output digital signals, delay the signals in units of lines, and output the digital signals by rearranging the signals, wherein when the monochromatic mode is set in the mode setting circuit, the line delaying/rearranging units can receive the digital signals, which are divisionally output from the monochromatic sensor and subjected to analog-to-digital conversion by the monochromatic analog-to-digital converter and the color analog-to-digital converters, and output the digital signals by rearranging the signals.
When the color mode is set in the mode setting circuit, the line delaying/rearranging units can receive the digital signals, which are output from the color sensors and subjected to analog-to-digital conversion by the color analog-to-digital converters, and output the digital signals by rearranging the signals.
The number of divided outputs from the monochromatic sensor can be larger than the number of outputs from the color sensors.
The monochromatic sensor can divide the signal by a number four times the number of the color sensors and output the divided signals.
The monochromatic sensor can be placed closer to one end face of the sensor unit than the color sensors.
The sensor unit can be set such that when an original is read in a forward direction, the monochromatic sensor reads a position on the original, which leads positions read by the color sensors.
The apparatus can further comprise a read direction setting unit for setting an original read direction to one of a forward direction and a reverse direction, wherein in accordance with one of the forward direction and the reverse direction set in the read direction setting unit, the line delaying/rearranging units can switch a line delaying and pixel rearranging process in the forward direction and a line delaying and pixel rearranging process in the reverse direction.
An image reading method of the present invention performs image processing by using a line sensor unit including a monochromatic sensor for outputting a one-line signal by dividing the signal into a plurality of signals, and a plurality of color sensors, a monochromatic analog-to-digital converter which corresponds to the monochromatic sensor and receives signals and performs analog-to-digital conversion for the received signals, and a plurality of color analog-to-digital converters which correspond to the plurality of color sensors and receive signals and perform analog-to-digital conversion for the received signals, wherein when a monochromatic mode rather than a color mode is set, the plurality of output signals from the monochromatic sensor are distributed to the monochromatic analog-to-digital converter and the color analog-to-digital converters to cause the monochromatic and color analog-to-digital converters to perform analog-to-digital conversion for the signals.
When the color mode is set, output signals from the color sensors can also be supplied to corresponding ones of the color analog-to-digital converters to cause the color analog-to-digital converters to perform analog-to-digital conversion for the signals.
Line delaying/rearranging units corresponding to the monochromatic analog-to-digital converter and the color analog-to-digital converters can be used to receive output digital signals, delay the signals in units of lines, and output the digital signals by rearranging the signals, and when the monochromatic mode is set, only the divided output signals from the monochromatic sensor can be used to rearrange digital signals subjected to analog-to-digital conversion by the monochromatic analog-to-digital converter and the color analog-to-digital converters.
When the color mode is set, the digital signals, which are output from the color sensors and subjected to analog-to-digital conversion by the color analog-to-digital converters, can be rearranged by using the line delaying/rearranging units.
When an original read direction is set to one of a forward direction and a reverse direction, in accordance with one of the forward direction and the reverse direction set as the read direction, the line delaying/rearranging units can switch a line delaying and pixel rearranging process in the forward direction and a line delaying and pixel rearranging process in the reverse direction.